Appendix B: About Wireless LANs
This appendix provides some background information about using wireless LANs (WLANs) and describes the following:
•Modes for Wireless LANs
•Basic Service Set (BSS) and Extended Service Set (ESS)
•Wired Equivalent Privacy (WEP)
Modes for Wireless LANs
Wireless LANs can work in either of two modes:
•Ad hoc Mode
•Infrastructure Mode
Ad hoc Mode
Ad hoc mode does not require an access point or a Wired (Ethernet) LAN. Wireless stations (such as notebook PCs with Wireless cards) communicate directly with each other.
Infrastructure Mode
In Infrastructure mode, one or more access points are used to connect Wireless stations (such as notebook PCs with Wireless cards) to a Wired (Ethernet) LAN. The Wireless stations can then access all LAN resources.
Note: Access points can only function in Infrastructure mode, and can communicate only with Wireless stations which are set to Infrastructure mode.
Basic Service Set (BSS) and Extended Service Set (ESS)
The following section describes the following types of wireless stations and the wireless channel:
•BSS
•ESS
•Channels
BSS
A group of wireless stations and a single access point, all using the same ID (SSID), form a Basic Service Set (BSS).
Note: Using the same SSID is essential. Devices with different SSIDs are unable to communicate with each other.
ESS
A group of wireless stations and multiple access points, all using the same ID (ESSID), form an Extended Service Set (ESS). Different access points within an ESS can use different channels. In fact, to reduce interference, it is recommended that adjacent access points use different channels.
As wireless stations are physically moved through the area covered by an ESS, they will automatically change to the access point which has the least interference or best performance. This capability is called Roaming. (Access points do not have or require roaming capabilities.)
Channels
The wireless channel sets the radio frequency used for communication.
•Access points use a fixed channel — Users select the channel used. This allows choice of a channel that provides the least interference and best performance. In the USA and Canada, 11 channels are available. If using multiple access points, it is better if adjacent access points use different channels to reduce interference.
•In Infrastructure mode — Wireless stations normally scan all channels, looking for an access point. If more than one access point is available, the one with the strongest signal is used. (This can only happen within an ESS.)
•If using Ad hoc mode (no access point) — All wireless stations should be set to use the same channel. However, most wireless stations
